The present invention is directed to an indicating device, which utilizes a light valve unit such as the liquid crystal cell in conjunction with a fluorescent plate and has a contrast filter and reflector arranged behind the unit and plate when taken in a direction of viewing.
A fluorescent activated display, which is referred to as a FLAD and utilizes an electro-optical light valve unit such as a liquid crystal cell in conjunction with a plate containing fluorescent particles, is known and examples are disclosed in German OS No. 26 16 669, whose disclosure was included in the U.S. Pat. No. 4,142,781 and also disclosed in German OS No. 26 19 352 on which U.S. Pat. No. 4,111,534 is based.
One version of a FLAD may have the light valve unit optically integrated with the fluorescent body so that it becomes a part of the light trap formed by the fluorescent body. A second version of a FLAD has the light valve unit and fluorescent part or plate spaced or separated without the optical coupling. A version with the optical coupling between the fluorescent plate and the light valve unit has several advantages over the version without the coupling. These advantages are that the fluorescent body does not require any special exit windows for decoupling light, polarizers can be eliminated, the fluorescent light may be decoupled from the body in those areas that are selected, and the excitation plate can be captured over a larger surface area. Despite these favorable conditions, the previously obtained representation quality still left something to be desired. For example, when only the front side of the display was available as a collector surface, the image contrast was still quite weak. An additional problem is that the diffused light, which is given off by the display, is often distributed over too large of a solid angle range and thereby reduces the contrast even more.